1. Field of the Invention
This invention relates to a robot controller and its control method. In particular the invention relates to improved robot controllers using generic personal computer operating systems that execute the processing associated with the occurrence of events on a real time basis.
2. Description of the Related Art
Most conventional robot controllers and their control methods are designed to control the operation of specific manipulators such as SCARA-type manipulators and cartesian coordinate manipulators. For these purposes the conventional robot controllers employ independently developed robot control operating systems ("OS").
In recent years, however, there has been an increased demand for robot controllers that are capable of controlling the entire system, such as controlling peripheral devices or communicating with external devices, beyond controlling the operation of manipulators. In such cases, an OS that incorporates a multi-tasking function must be used as a robot controller OS. To meet this need either proprietary OS or generic real time operating systems (pSOS, VxWorks, VTRX, OS-9, etc.) are used in most cases.
It should be noted that "pSOS" is a registered trademark of Integrated Corporation, "VxWorks" is a registered trademark of WindRiver Systems Corporation, and "VRTX" is a registered trademark of MicroTech Research Corporation.
Because the control of manipulators and peripheral devices requires real time processing, an important requirement for a robot controller OS is the ability to ensure real time processing.
The development of proprietary operating systems capable of ensuring real time processing requires a vast amount of labor. On the other hand, while generic real time operating systems provide such real time processing capabilities, their high cost can be an economic drawback.
Recently, low-cost, high functionality personal computer operating systems have become available and are widely used. If such a personal computer operating system can be used for a robot controller, it is possible to achieve both substantial reductions in developmental labor and costs. This approach offers the additional advantages of ease of training from the standpoint of users, further reductions in developmental leadtimes because of the availability of a full complement of developmental tools, and the possibility of extending applications through the use of off-the-shelf hardware and software.
However, even though low-cost personal computers and PC-oriented operating systems offer multi-tasking capabilities, their task-switching operations are slow. A reduction in switching intervals is impossible, and it is therefore difficult to ensure real time processing.
As noted previously, because the control of manipulators and peripheral devices in a robot controller requires real time processing, if an operating system takes a long time between the occurrence of an event and the startup of the task that processes the event, the system falls short of being fully practical for a robot controller.
Another complicating factor is that, if any of the aforementioned personal computers or PC-oriented operating systems is used, the length of time between the occurrence of an event and the startup of the task that processes the event can vary greatly depending on the timing at which the event occurs. This fact tends to reduce the quality of the processing in terms of reproducibility.